The deaths of at least 60 Palestinians in protests along the Gaza border are "tragic and extremely concerning", the Prime Minister has said.
Speaking alongside Turkish President Recep Tayyip Erdoğan who earlier branded the deaths by Israeli army fire a "horrible massacre", which the opening of the new US embassy in Jerusalem had "paved the way for", Theresa May called on all sides involved in the conflict to show restraint.
At a joint press conference following talks at Downing Street, Mrs May called the situation in Gaza and the West Bank "troubling", adding that the violence was "destructive to peace efforts" and called on Israel to "show restraint".
She continued: "There is an urgent need to establish the facts of what happened yesterday through an independent and transparent investigation, including why such a volume of live fire was used and what role Hamas played in events.
"Palestinians have the right to protest, but these protests must be peaceful.
"We are concerned that extremist elements are seeking to hijack legitimate protests to further their own objectives."
Meanwhile Mr Erdoğan said that Turkey had recalled its ambassador to Israel over the deaths, and would not accept the US decision to move its embassy from Tel Aviv to Jerusalem which "ignored the resolutions of the UN and international law".
As well as the deaths, which were mostly caused by gunfire, more than 2,700 Palestinians were injured as they demonstrated on the anniversary of the creation of the State of Israel and the opening of the new US embassy in Jerusalem.
But speaking at the UN, the US Ambassador Nikki Haley told the Security Council that no member "would act with more restraint than Israel has" in its confrontation with Palestinians at the Gaza border.
She said that the deaths had nothing to do with the opening of the US embassy, and that the Islamic militant group Hamas that rules Gaza has been inciting violence there for years.
Ms Haley said that the opening of the new embassy in the "capital of Israel" was a "cause for celebration for the American people", as it was the "right thing to do" and "reflected the will of the American people".
She added that there was no "plausible peace agreement in which Jerusalem would no longer be recognised as the capital of Israel", and accepting this would make peace "more achievable, not less".
Earlier on Tuesday, Boris Johnson told the Commons that the "peaceful protests" had been “exploited by extremists”, but urged Israel to show restraint in using live fire.
The Foreign Secretary issued his plea as he insisted the UK remains committed to a two-state Israel-Palestine solution with Jerusalem as the shared capital.
Israel and Palestine both contest the city of Jerusalem which is also of great importance to both Judaism and Islam.
Shadow foreign secretary Emily Thornberry joined Mr Johnson in condemning the violence and also called on him to draft a statement to the UN Security Council calling for an "urgent, independent investigation into the violence in Gaza, to assess whether international laws have been broken and to hold those responsible to account".
She continued there had been an apparent “calculated and deliberate policy to kill and maim unarmed protesters, who posed no threat to the forces on the Gaza border.
“Many of them shot in the back. Many of them shot hundreds of metres from the border, and many of them children.”
On Tuesday, Palestinians were observing a general strike to mourn those killed in the deadliest day in Gaza since the 2014 war.
Organisers said the day would be set aside for funerals and that turnout for any new protests on the border with Israel would be low.
Despite the 58 deaths, which included a number of children, Israel's ambassador to the UK maintained that his country's forces used live fire in a “measured” and “surgical” way.
He also claimed Israel “did everything we could” to avoid the bloodshed at the border with Gaza, which saw soldiers open fire on protesters.
The diplomat insisted that the protests were organised by militant group Hamas with an aim to “breach the border, to get inside Israel and to kill Israeli citizens”.
On Tuesday, Labour leader Jeremy Corbyn called for the UK to "review arms sales to Israel while these violations continue", adding that "we cannot turn a blind eye to such wanton disregard for international law".
However, speaking in the Commons, Middle East minister Alistair Burt said that Britain had so far received “no information” to suggest that UK-supplied equipment has been used against protesters, amid calls from opposition MPs to suspend arms sales to Israel.
He also said the tragedies should be used as “an opportunity for a springboard to peace”.
Responding to Mr Burt's statement, Tory former minister Andrew Percy urged him to continue to “differentiate between protesters and between those who have used children as shields at the border, and those who have gone to the border with the sole intention of breaching it to kill innocent civilians”.
Fellow Conservative Ross Thomson added: “We have seen Hamas officials actively encouraging protesters to be martyrs, bussing rioters to the border for them to sling Molotov cocktails and fire bombs across it to tear down fencing.”
He asked if Mr Burt shared his concern that Hamas are “using civilians as a cover to incite violence”.
The minister replied: “The horror with which people might be prepared to encourage more blood in order to demonstrate a political point is very real in the area – if there is anything we can do, we have to break into that as those who have done in other areas of conflict.”
On Monday, Theresa May said she was “extremely concerned” by the scale of the violence, describing the loss of life and injuries to the Palestinians as “tragic”, and urged both sides to “show restraint and refrain from any further violence”.